It happens, at this moment, that there is an extraordinary demand for emigration; that every letter from Australia calls for a supply of human life, and especially for an emigration of females,--the proportion of males to females in some of the settlements being 9 to 1, while the number of females predominates, by the last census in England. There is a daily demand for additional labourers, artificers, and household servants, and with offers of wages which in England neither labourer nor artisan could hope to obtain. Thousands are now offered employment, comfort, and prospective wealth in Australia, who must burthen the workhouse at home. The advantages are so evident, the necessity is so strong, and the opportunity is so prompt and perfect, that they _must_ result in a national plan of constant emigration, until Australia can contain no more--an event which may not happen for a thousand years. It happens, also, by a striking coincidence, that Australian discovery has just assumed new vigour; and that instead of the barrenness and deformity which were generally supposed to form the principal characteristics of this vast territory, immense tracts have been brought to European knowledge for the first time, exhibiting remarkable fertility, and even the most unexpected and singular beauty. We now give a sketch of the journey in which those discoveries were made. To explore the interior of this great country has been the object of successive expeditions for the last five-and-twenty years. But such was the want of system or the want of means, that nothing was done, except to increase the tales of wonder regarding the middle regions of Australia. The theorists were completely divided; one party insisting on the existence of a mediterranean or mighty lake in the central region, _because_ there was a tendency in some of the small rivers of the coast to flow inward. Others, with quite as much plausibility, laughed at the idea; and, from having felt a hot wind occasionally blowing from the west, had no doubt that the central region was a total waste, a desert of fiery sand, an Australian Sahara! while both parties seem to have been equally erroneous, so far as any actual discovery has been made.